Multi-port flow control valves

ABSTRACT

Multi-port flow control valves are provided wherein the outlet ports may be opened in cascade fashion to allow fluid to flow through the outlet ports into at least two conduits in which the opening of the outlet ports is controlled by a signal indicating the need for fluid in the conduits. The valves are particularly useful for controller the supply of heating/cooling fluid to multiple heating/cooling coils employed to control reactions. In a preferred embodiment the opening of the ports is controlled according to the heat measured in the reaction

The present invention relates to valves and in particular to valveswhich may be used to control the delivery of fluids, gases and/orliquids in a cascade fashion to two or more conduits. The invention isparticularly useful in the delivery of temperature control fluidsespecially to chemical reactors which employ multiple cooling elementsto provide a variable area heat transfer control system.

PCT Patent applications PCT/EP02/04651, PCT/EP02/04646, PCT/EP02/04650and PCT/EP02/04648 describe a system for measuring heat liberated orabsorbed by a chemical or physical reaction. This information can beused for measuring and controlling reaction efficiency in steady stateprocesses and reaction progress in unsteady state processes. The controlis affected by measuring the temperature change in the heat transferfluid to determine the quantity of heat liberated or absorbed by thereaction and adjusting the area of temperature control surface availableto the reaction accordingly.

The earlier patent applications describe a system containing a series ofheat transfer coils where individual heat transfer coils are designedsuch that the heat transfer area of the heat transfer pipe is matched(approximately given that U varies with flow, temperature and liquidproperties and it varies with application) with the flow carryingcapacity of the liquid such that:U.A.LMTD=m.Cp.(t _(si)-t _(so))(kW)where U=overall heat transfer coefficient (kW.m⁻².K⁻¹)

-   -   A=heat transfer area (m²)    -   m=mass flow rate of heat transfer fluid (kg/s)    -   LMTD=log mean thermal difference between service and process        fluids (° C.)    -   Cp=specific heat of heat transfer fluid (kJ.kg⁻¹K-⁻¹)    -   (t_(si)-t_(so))=temperature (° C.) change in the heat transfer        fluid between inlet and outlet

The system described in PCT Patent applications PCT/EP02/04651,PCT/EP02/04646, PCT/EP02/04650 and PCT/EP02/04648 is a variable areaheat transfer system. Multiple coils are used in combination to matchthe desired operating conditions. The ability to transition betweenthese coils in a smooth, bounce-less manner is of great importance tothe stability of the system. Poor accuracy of the heat measurements canresult from a crudely implemented system. The system described in thePCT Patent applications PCT/EP02/04651, PCT/EP02/04646, PCT/EP02/04650and PCT/EP02/04648 utilizes multiple control and switching valves tobring individual coils into or out of operation. This is however acomplicated system which can involve jumps in the system as one switchesa new coil into action or as one switches a coil out of action. The useof a multi-port flow control valve, which whilst achieving a high degreeof control also offers the additional benefits of a compact design,reduces the amount of control signals required and enables smoothertransitions.

The present invention therefore provides a valve for the control of thedelivery of fluids to two or more conduits in a cascade fashion whereinthe valve has multiple outlet ports operating in a cascade wherein theoutlet ports are opened and/or closed according to a signal expressingthe requirement for fluid in the conduits.

The multi-port flow control valve of the present invention is unlikeconventional control valves in that whereas most conventional controlvalves will have a single inlet and a single outlet port, this valvewill preferably have a single inlet, and multiple outlet ports operatingin a cascade fashion as the valve is modulated. Some control valves,such as the Baumann model 2400 Little Scotty 3-way control valve (asdescribed in U.S. Pat. No. 4,434,965) do have more than one inlet oroutlet port. The Little Scotty is however designed for use as adiverting or mixing valve; as such several valves arranged in a cascadewould be needed to provide heat transfer fluid for the control of avariable area reactor, but the use of multiple valves is of no benefitwhen compared to a system based on conventional control valves.

The valves of the present invention and their use for the control of theflow of heat transfer fluids for temperature control in a reactor isillustrated in the accompanying drawings in which:

FIG. 1 is a schematic illustration of a multi-valve control system asemployed in PCT Patent Applications PCT/EP02/4651, PCT/EP02/04646,PCT/EP02/04650 and PCT/EP02/04648.

FIG. 2 is a schematic illustration of the system of FIG. 1 in which themulti-valve system has been replaced by a multi-port control valveaccording to the present invention.

FIGS. 3 and 4 illustrate a valve operated in a linear fashion and showshow the outlet ports may be shaped and configured according to the needsof the system.

FIGS. 5 shows a multi-port control valve operated in a rotary fashion.

FIG. 1 shows a chemical reactor (1) provided with a series ofheating/cooling coils (2 to 7). The flow of heat transfer fluid to eachcoil is selected by separate valves (8 to 13). The flow rate to theselected coils is controlled by valve (14). This system is asillustrated in and operates in the manner described in PCT PatentApplications PCT/EP02/04651, PCT/EP02/04646, PCT/EP02/04650 andPCT/EP02/04648.

FIG. 2 shows the same reactor (1) with the same heat transfer coils (2to 7) but the valve system (8 to 13) and control valve (14) has beenreplaced by a single control valve (15) which has a single inlet line(16) and multiple outlet ports (17 to 22). In operation the outlet portsmay be opened or closed in a cascade fashion to enable fluid to flowinto selected cooling coils or to cut off the flow of fluid intoselected coils. The position of the plunger (23) is determined by theactuator (24) in response to a signal supplied by the control system.Indeed the plunger may be positioned to partially block an outlet portif full flow is not required to that particular coil.

FIGS. 3 and 4 illustrate alternate configurations for the outlet portsand show how the outlet ports may be progressively opened and closed tothe fluid supplied through the inlet port by the movement of the plunger(23). It can be seen from FIGS. 3 and 4 that the relative positioningand shape of the outlet ports can be designed to enable a smooth controlof the flow of heat transfer fluid to the coils. The C_(v) of eachindividual orifice can be characterised to match each particular coilsflow requirements in a similar way to that of a conventional controlvalve.

FIG. 5 shows an alternate form of a valve according to the presentinvention in which the outlet ports (25 to 30) may be opened and closedto the fluid supplied through inlet port (31) by rotation of a cam (32)by the actuator (33). The relative positioning and shape of the outletports can again be designed to enable smooth control of flow of heattransfer fluid to the coils. The sizes and shapes of the outlet portswill again be similar to those used for the linear version illustratedin FIGS. 3 and 4.

The valves of the present invention therefore can be designed to providethe same control characteristics as a conventional control valve foreach of its multiple outlet ports and as such can be used to replacemultiple conventional valves with a single multi-port flow valve havinga single means of activation requiring at least one control signal onlyas opposed to multiple valves and actuators and one control signal percontrol valve.

A multi-port flow control valve of the present invention can thereforebe constructed to operate either with a linear or rotary action. Thenumber of outlet ports will depend on the number of individual flows,which need to be independently controlled. In the example illustrated inFIG. 2, 6-heat transfer coils are used, but the valve of the presentinvention can be designed for use with any number. By modulating themulti-port flow control valve the effective heat transfer area in thereactor can be varied. The maximum number of outlet ports on this typeof valve is limited only by the physical constraints of theconstruction. Similarly the use of a multi-port flow control valve isnot limited to variable area reactors and could equally be used forother similar applications.

When used with a variable area reactor improved control of the flow toeach coil can be achieved by characterising the individual outlet ports.This is achieved by designing each outlet port to a specific size andprofile. Any combination of port sizes and profiles can be used,dependent on the specific C_(v) and flow characteristics required. Byoverlapping the outlet port profiles, smooth and bump-less transitionscan be made between each variation in heat transfer area. A similarvalve, which does not have overlapping outlet port profiles, can be usedand may still provide acceptable results in certain circumstances. FIG.3 illustrates a typical overlapping port arrangement of a 6-port linearvalve. In this example different width slots have been used to extendthe range and turn down of the valve. FIG. 4 shows a second typicalarrangement, but in this instance different port profiles provide adifferent overall characteristic. By varying the number of ports andport profiles, the only restrictions to the infinite number ofcharacteristics achievable are the physical size restrictions of thehardware.

Any material may be used to construct a multi-port flow control valve,providing that it is resistant to corrosion and wear from the liquid orgas it controls.

In its linear form the multi-port flow control valve has an internalplunger, which regulates the flow according to a control signal given toa linear actuator by the control system. In the case of a rotary valve,an internal cam is used to block off the unused ports in a cascadefashion (a ball, plug, disc, globe etc. can be used in place of thecam). The cam or piston can be positioned (in response from a signal tothe control system) to partially block off any one or of the outletports. Thus a fine level of smooth bounce-less control can be achievedwith either the linear or rotary valve.

Actuation of either variant (linear or rotary) of the multi-port flowcontrol valve can be achieved with any of the established valve actuatortechniques. This includes, but is not limited to: pneumatic, hydraulic,electric, linear transformer etc.

Whilst the valves of the present invention may be used in any systemwhich involves delivery of fluids to two or more conduits it isparticularly useful in the supply of heat transfer fluids to thevariable area heat transfer systems in reactors described in PCT PatentApplications PCT/EP02/04651, PCT/EP02/04646, PCT/EP02/04650 andPCT/EP02/04648. These reactors may be used in any processes involvingphysical or chemical change in which heat is released or absorbed. Itsuse will therefore be illustrated in relation to such a system.

In its preferred application the invention is used in connection withvariable area heat transfer systems used to improve the ability tomonitor the progress of physical and/or chemical reactions, it is alsoused in connection with improving the control of reaction systemsthrough the improved monitoring. The improved control of the flow ofheat transfer fluid that is provided by the present invention enablesthe production of materials of higher quality and purity, it enablesmore efficient use of reaction equipment and can further improve theefficiency of the equipment so that shorter reaction times are needed toobtain a given amount of material from a given amount of startingmaterials. Another advantage is that smaller reactors may be used toproduce a given volume of material.

Many reactions are hazardous and care needs to be taken to ensure noaccidents. The more accurate and more timely control of the reactionprovided by this invention enables reactions to be performed withinstricter limits. This enhances safety and can reduce the reactioninefficiencies that, hitherto, were an inherent shortcoming of themanufacturing process.

Reactions whether they be physical, chemical or both generate or absorbheat and there is therefore a heat change across the reaction. Thetheoretical heat generated or absorbed in a particular reaction is knownfrom established information. The actual heat generated or absorbedduring the course of a reaction could therefore, in theory, be a usefulmeasure to determine reaction efficiency in the case of steady statereactions and reaction progress in the case of batch reactions.

By way of an illustration of the theory, a typical chemical synthesisstep will be considered. Two reagents (A and B) react together to form anew compound (C) as follows:A+B→Cwhere A=kmol of A

-   -   B=kmol of B    -   C=kmol of C

The heat generated by this reaction is established according to theformula:Q=ΔHr.C(kJ).where ΔHr=heat of reaction per kmol of C produced (kJ/mol)

-   -   C=kmol of component C produced (kmol)

The value of ΔHr may be determined from theoretical data or laboratorycalorimeters.

Currently the heat data described may be used in a variety of ways.

For any reaction, the maximum theoretical heat liberation can becalculated as follows:Q′=ΔHr.C′ (kJ)where Q′=maximum theoretical heat generated (kJ)

-   -   ΔHr=heat of reaction per kmol of C produced (kJ/kmol)    -   C′=maximum theoretical yield of component C (kmol)

The maximum theoretical yield C′ is based on the assumption that one orboth of the feed components (A and B) are completely consumed.

If the heat of reaction is measured during a process, the quantity ofcomponent C synthesised at any time is as follows:C=Q/ΔHr(kmol)where C=quantity of C produced (kmol)

-   -   Q=heat measured during the reaction (kJ)    -   ΔHr=heat of reaction per kmol of C produced (kJ/kmol)

Thus the total mass of C can be calculated by knowing the total heatabsorbed or liberated and the heat of reaction (or crystallisation etc).

The expected theoretical yield of C is known from the quantity ofreactants present and the stoichiometry of the process. Thus from theinformation above, the percentage conversion can be determined from theequation below.η=C/C+×100where η=percent conversion

-   -   C=quantity of C produced (kmol)    -   C+=maximum theoretical yield of component C (kmol)

In batch reactions, percent conversion (η) provides an effective meansof identifying reaction end point. This can be used to reducemanufacturing time and improve plant utilisation.

In continuous (plug) flow reactors, reaction efficiency (η) provides aparameter for controlling feed rate to the reactor and controllingprocess conditions. In this way it is possible to run conventional batchprocesses in small-scale plug flow reactors. This benefits all aspectsof the manufacturing process including lower capital cost for equipment,increased plant versatility, improved product yield, safer processconditions (through smaller inventories), greater product throughput andreduced product development time.

The ability to monitor reaction progress has an additional safetybenefit for both small and large reactors. A system with onlinecalorimetric data can instantly identify when unreacted compound isaccumulating in the reactor. This reduces the risk of runaways due toaccumulation of unreacted chemicals.

The design of reactors in common industrial use is however inherentlyunsuitable for measuring calorimetric data and thus the techniquesdescribed remain theoretical.

Chemical reactors in common use in, for example, the pharmaceutical andfine chemical industries fall into four main categories. Standard batchreactors in which reagents are mixed in a stirred vessel in which heatis added or removed by means of heat transfer fluid recirculating thoughan external jacket. These are the most commonly used reactors forsmall-scale organic and inorganic synthesis reactions. Batch reactorswith internal coils, which are a variation on the standard batch reactorand have additional heat transfer surfaces within the body of theliquid. These reactors are used for general-purpose batch reactionswhere higher heat loads are encountered. Loop reactors in whichreactants are pumped through an external heat exchanger and returned tothe vessel. These are commonly used for gas/liquid reactions in whichcase the liquid is returned to the reactor via a spray nozzle to createa high gas/liquid interfacial area. Continuous reactors in whichreactants are pumped through a heat exchanger under steady stateconditions. These are generally used for larger scale manufacturingprocesses with long product runs.

The heat transfer characteristics of the four types of reactorsdescribed above have three common features:

-   -   i. The heat transfer fluid is circulated through the heat        exchangers at high velocity to maintain favourable heat transfer        coefficients. In the case of jacketed reactors, this is achieved        by injecting the heat transfer fluid into the jacket at high        velocities using nozzles or diverting flow around the jacket        with baffles. In some instances, coils for the flow of heat        transfer fluid are welded to the outside wall of the reactor        vessel.    -   ii. High mass flow rates of heat transfer fluid are employed to        maintain a good average temperature difference between the heat        transfer fluid and the process fluid.    -   iii. The heat transfer area is fixed and temperature control of        the process fluid is achieved by varying the temperature of the        heat transfer fluid. In some cases limited scope exists for        increasing or decreasing the heat transfer area.

The features described above represent good design practice forachieving a flexible and optimised heat transfer capability within thereactor. However, these features do not lend themselves to measuring thequantity of heat generated or liberated or to the use of the measurementof the heat generated or liberated to control the flow ofheating/cooling fluid to provide improved control of the reaction. Thisdeficiency is illustrated by reference to the chemical reaction betweenreagents A and B as discussed above. (It should be noted that theExample is not limited to chemical reactions and is equally applicableto other chemical and physical processes).

When the two reagents (A and B) react together to form C, heat isliberated. The heat liberated per second can be expressed as follows:q=ΔHr.c(kW)where q=heat liberated per second (kW)

-   -   ΔHr =heat of reaction per kmol of C produced (kJ/kmol)    -   c=kmols of component C produced per sec (kmol/s)

If the process temperature remains constant the heat liberated (q) willbe observed as a temperature rise in the heat transfer fluid accordingto the formula.q=m.Cp(t _(si)-t _(so))(kW)where q=heat liberated by the reaction (kW)

-   -   m=mass flow rate of the heat transfer fluid (kg/s)    -   Cp=specific heat of heat transfer fluid (kJ.kg⁻¹K⁻¹)    -   t_(si)=temperature of heat transfer fluid in (° C.)    -   t_(so)=temperature of heat transfer fluid out (° C.)

However, in order to determine q, the flow rate and temperature changeof the heat transfer fluid (t_(si)-t_(so)) must be measured accurately.In the reactor examples described above, effective design favours highflow rates of heat transfer fluid. Often this leads to a temperaturechange of the heat transfer fluid (t_(si)-t_(so)) of less than 1° C. AnIEC Class A RTD is one of the more accurate temperature measurementdevices available. These devices have a tolerance of ±0.25° C. (theerror on the installed device may be higher). Thus for a temperaturechange of 1° C., the accuracy of heat measurement can be expected to be±95% or worse. This would rise to 250% where the heat transfer fluidtemperature changed by 0.1° C. This factor alone makes it virtuallyimpossible to measure the heat of reaction in conventional reactorswhich, in turn, makes it difficult to accurately control the flow ofheating/cooling fluid. Furthermore, on a conventional reactor, heatleaking out of the system via the non-process side of the jacket cancreate serious error.

Furthermore, conventional chemical reactors often have sluggish controlsystems which permit temperatures of the bulk material to cycle by a fewdegrees. In energy terms a few degrees change in temperature canrepresent a significant proportion of the overall energy release.

Conventional reactors offer acceptable heat transfer characteristicswhen the flow of heat transfer fluid is held at a good velocity. Sincethe heat transfer surface is limited to 1 or 2 discrete elements, therange (of energy liberated or absorbed) over which a useful servicetemperature rise (t_(si)-t_(so)) can be achieved is very limited. In acase where the energy release from the process is small, the temperaturerise in the heat transfer fluid may be a fraction of a degree. Inaddition to this, the shaft energy of the heat transfer pump could be ahigh proportion of the total.

The limitations described above are common to all reactors (andevaporators, batch stills etc) used in the pharmaceutical, chemical andallied industries. Accordingly, when employing these reactors the heatgenerated or consumed by the reaction cannot be used to monitor andcontrol the progress of a reaction within any degree of accuracy.

PCT Patent applications PCT/EP02/04651, PCT/EP02/04646, PCT/EP02/04650and PCT/EP02/04648 provide various aspects of reaction systemscomprising a reactor containing a reaction process medium and a heatexchanger comprising at least two conduits through which flows a heattransfer fluid. In the processes of these patent applications,measurement of the flow rate and temperature change of the heat transferfluid across the reaction is used to determine the heat generated orabsorbed by the reaction system and that determination is used tomonitor and control the reaction by varying the area of the heatexchanger available to the reaction process medium. As stated in theseapplications, this can be effective providing

-   -   i. the average temperature difference between the heat transfer        fluid and the processes fluid is from 1 to 100° C.    -   ii. the temperature differential (t_(si)-t_(so)) of the heat        transfer fluid across the reaction system is at least 1° C.    -   iii. the linear velocity of the heat transfer fluid is at least        0.1 meters/second.

Providing these criteria are satisfied measurement of the flow rate andtemperature change of the heat transfer fluid across the reactionenables the heat generated or absorbed by the reaction system to bedetermined with a high degree of accuracy over a wide range of operatingconditions. The determination may then be used to monitor the reactionwith a high degree of accuracy. The valve system of the presentinvention may then be operated according to this determination to enablethe ports which provide fluid to the coils to be opened and dosed in asmooth cascade fashion.

Whilst any form of conduit may be used for the heat exchanger, pipes orcoils are preferred.

PCT Kingdom Patent applications PCT/EP02/04651, PCT/EP02/04646,PCT/EP02/04650 and PCT/EP02/04648 in order for effective operation ofthese monitor and control systems the reaction system should preferablyhave the following characteristics:

-   -   a. The heat exchanger should have sufficient surface area to        ensure that a measurable temperature difference (t^(si)-t_(so))        is observed in the heat transfer fluid as it passes across the        reactor. For the purposes of accuracy, a temperature difference        of more than 1° C. (more preferably more than 10° C.) is        desirable.    -   b. A high temperature difference is preferably maintained        between the process fluid and the inlet heat transfer fluid        (t_(si)) to ensure that an accurately measurable service fluid        temperature change (t_(si)-t_(so)) can be achieved and smaller        heat transfer areas are required.    -   c. As far as possible, heat must only be transferred to or from        the process fluid and not be transferred to other equipment or        the environment    -   d. The heat transfer fluid must always flow at a reasonable        velocity. The velocity will vary with coil size and conditions        but it is preferred that it is greater than 0.1 m/s more        preferably greater than 1 m/s. Lower velocities will give slower        temperature control response. Low velocities also give a higher        ratio of thermal capacity (of the heat transfer fluid) to heat        release rate. This will compound errors in the values of        measured heats.    -   e. When used for batch processes or multi-purpose duties, the        heat transfer equipment should be capable of stable operation        over a wide range of energy release/absorption rates. The range        will vary according to the nature of the reaction. In the case        of batch reactions a very wide operating range will be required.

To satisfy condition c above, the heat exchanger is preferably immersedin the process fluid and should be fully insulated at all points otherthan where fully immersed in the process fluid. This ensures that allthe heat gained or lost by the heat transfer fluid is transferreddirectly from and to the process fluid. This condition is most easilyachieved by designing the heat exchanger as a coil or coils fullyimmersed in the process fluid.

It is further preferred that an optimal relationship between heattransfer surface area to heat transfer fluid flow capacity is provided.Such conditions exist when the heat transfer fluid (traveling at thedesired linear velocity) provides an easily measured temperature change(such as 10° C.) without incurring excessive pressure drop. It should benoted that the optimum heat transfer conditions vary according to theproperties of the process fluids and heat transfer fluids respectively.The valve system of the present invention enables the smoothintroduction and removal of coils thus providing a smooth control of theavailable heat transfer surface area.

In order to satisfy these criteria, the heat exchanger for the reactoris preferably a heat transfer coil, which preferably passes through thereaction fluid. The design of the coil is important to achieving theobject of the invention and must be such that the heat transfer areamatches the heat carrying capacity under specified conditions.

The valves of the present invention may be used in systems in which theheat transfer fluid is straight through or recycled.

In the preferred reactors with which the present invention is used theheat transfer area of a coil may be related to the flow carryingcapacity of the liquid by using the formulaU.A.LMTD=m.Cp.(t _(si)-t _(so))(kW)where U=overall heat transfer coefficient (kW.m⁻².K⁻¹)

-   -   A=heat transfer area (m²)    -   m=mass flow rate of heat transfer fluid (kg/s)    -   LMTD=log mean thermal difference between service and process        fluids (° C.)    -   Cp=specific heat of heat transfer fluid (kJ.kg⁻¹K⁻¹)    -   (t_(si)-t_(so))=temperature (° C.) change in the heat transfer        fluid between inlet and outlet

This information may then be used to determine the optimum diameter tolength relationship of an individual coil whereby high turbulence isachieved without incurring excessive pressure drop of heat transferfluid through the heat exchanger (as shown by a high Reynolds number).In the preferred system the following criteria apply:

-   -   a. The temperature difference between the inlet heat transfer        fluid and the process fluid should be large enough (e.g. 5-100°        C.) to ensure that the heat transfer fluid undergoes a        measurable temperature change (>1° C. or preferably greater than        10° C.) in its passage through the coil. The temperature change        must not however be so high or low as to cause freezing, waxing        out, boiling or burning of the process fluid.    -   b. The heat transfer area must be large enough to ensure that        the heat transfer fluid undergoes a measurable temperature        change (>1° C. or preferably greater than 10° C.) through the        process fluid. Smaller temperature changes limit heat transfer        capacity and accuracy. Higher temperature changes are desirable        providing they do not cause freezing, waxing out, boiling or        burning of the process fluid.    -   c. The linear velocity of heat transfer fluid must be reasonably        high (preferably>0.1 m.s⁻¹) in order to maintain satisfactory        control response and a good overall heat transfer coefficient.    -   d. The pressure drop of heat transfer fluid flowing through the        coil is from 0.1 to 20 bar.

In practice, optimum coil lengths will vary according to the temperaturedifferences employed and the thermodynamic and physical characteristicsof the system. Calculating optimal coil length is an iterative process.A general-purpose device will be sized using conservative data based onfluids with low thermal conductivity and a low temperature differencebetween the reaction fluid and the heat transfer fluid. Each coil willhave a limited operating range.

In a preferred system in which the heat transfer equipment is capable ofstable operation over a wide range of energy releases, the system issuch that the area of heat transfer may be varied according to the needsof the particular reaction (or stage of reaction). This may beconveniently accomplished by providing multiple heat transfer pipes eachof which has a diameter and length relationship designed to provide acertain degree of heat transfer. The valve system of the presentinvention enable the pipes to be brought into and out of operation in asmooth cascade fashion as the needs of the reaction system dictates.

As the load increases the flow of heat transfer fluid to a coil (or setof coils) can be increased using a flow control valve of the presentinvention. In this way when the heat generation measurement indicatesthat an additional coil is required to accommodate a rising load, thecontrol valve will be activated to ensure smooth transition to thehigher flow. Use of a valve of the present invention will ensure a rapidand smooth flow control response to the step change in the systempressure drop. The use of the valve will provide a smooth transitionbetween operating conditions and enable a wide operating range employinga large number of coils.

Fast and accurate temperature measurements is important. To achievethis, the temperature element is conveniently mounted in fast flowingheat transfer fluid. A minimum hold up volume (of service liquid) shouldexist between the temperature elements and the heat transfer surface.This may be achieved by using sub manifolds on the discharge pipes asshown in FIG. 6.

FIG. 6 is a schematic illustration showing three differentialtemperature measuring devices (34), (35) and (36) on a seven-coil systembased on coils (37) to (43). These devices measure temperature change ofheat transfer fluid flowing across the coils. The temperature deviceswork in a cascade fashion. At low flow (coil 37 or coils 37 and 38operating) measuring device (34) is used for measuring dischargetemperature. When three or more coils are operating, measuring device(34) switches to idle and measuring device (35) takes over. When five ormore coils are operating, both (34) and (35) switch to idle andmeasuring device (36) takes over. This concept is applied irrespectiveof the number of coils and temperature devices used. It is preferredthat the linear velocity of the heat transfer fluid as it passes thetemperature element is one meter per second or greater (although slowervelocities can be tolerated). The temperature devices must be highlyaccurate and sensitive. It should be noted that separate inlet andoutlet temperature devices could be used as an alternative to thedifferential devices.

In a preferred process, in addition to the normal process temperaturetransmitters, which constantly measure the process across its entirerange and provide the necessary safety interlocks, a second pair oftemperature elements can be provided to monitor the specific process setpoint. The arrangement uses two different types of measuring elements.The main device is preferably an RTD, a 4 wire Pt100 RTD to {fraction(1/10)}^(th) DIN standard being especially suitable. The transmitterused to provide the 4-20 mA output signal is spanned to the minimumallowable for the transmitter (similarly any output signal type ortemperature span could be used). The temperature transmitter will becalibrated specifically at the process set point. Larger ranges willstill give acceptable results, but reducing the span to the minimumpossible offers improved accuracy and resolution. Thus this arrangementwill provide an extremely accurate means of process temperaturemeasurement.

The element of the temperature measurement system is the part of thedevice which is in contact with the liquid. In the case of an RTD, itsresistance will change in response to changing temperature. The responseof an RTD is not linear. The transmitter is the calibrated part of ameasuring device and is used to linearise the output to the controlsystem and convert the signal to an industry standard, usually 4-20 mA,but it could also be 1-5 V or 0-10V. A thermocouple's response to achange in temperature is a varying voltage. Usually milli volts per ° C.A thermocouple transmitter will again convert this signal to an industrystandard, again more often than not, 4-20 mA. Accordingly the term‘element’ when describing a physical mechanical presence in the process,e.g., a temperature element is located in the reactor and measures thetemperature of the reactor contents. And the term ‘transmitter’ whendescribing aspects of temperature measurement relating to the controlsystem, e.g., a temperature transmitter is calibrated 0-100° C. anddisplays the contents temperature of the reactor. It is the signal fromthe transmitter which is used to operate the valve of the presentinvention when used in this type of reactor system.

The limitation of any RTD is its speed of response to a step change intemperature. Typically it can take up to four or five seconds for an RTDto measure a change in temperature. Thermocouples, on the other hand,can respond much more rapidly to temperature fluctuations. For thisreason a thermocouple is also used to monitor the process set point, a Ttype thermocouple being especially suited. Its transmitter will besimilarly ranged to the RTD. However, as a T type thermocouple has anaccuracy of only + or −1° C., it will not be used to monitor the processtemperature. Its function is to monitor the rate of change of theprocess temperature.

The combined use of these two different types of sensing elementsprovides a temperature sensing system, which is extremely accurate; thisinformation may then be relayed to operate the valve of the presentinvention in response to the heat generated to provide a highlyresponsive reactor control system. It should be noted that not allprocess operations require this level of temperature measurementaccuracy and control. In such cases, more basic temperature control andmeasurement systems will prove tolerable.

In order to fully utilize this two-element approach, custom software isused to determine which process variable (temperature, or rate of changeof temperature) is the most significant at any one instance in time.

Accurate measurement of the flow of the heating/cooling fluid is alsoimportant for effective operation of the type of reactor systemdescribed in PCT Patent applications PCT/EP02/04651, PCT/EP02/04646,PCT/EP02/04650 and PCT/EP02/04648. FIG. 7 shows a flow measurementsystem for the reactor shown in FIG. 6 employing multiple flow devices.Flow device (44) is a low range device for measuring flow when coils(37) or coils (37) and (38) are in operation. When three or more coilsare in operation, flow device (45) takes over and (44) switches to idle.Any number of flow transmitters can be used to achieve satisfactoryaccuracy. As a general rule, the number of flow devices to be usedshould be calculated as followsNumber of flow devices=(F _(max)-F _(min))/(R.F _(min))where F_(max)=maximum flow (kg.s⁻¹)

-   -   F_(min)=minimum flow (kg.s⁻¹)    -   R=turn down ratio of the flow instrument

The above equation makes reference to mass flow. The equipment can use avolume flow device however provided the system converts volume flow datainto mass flow data. This can be done automatically by the controlsoftware (mass flow=volume flow×liquid density). For sensitive systems(or those with a wide temperature range) compensation should be made forchanges in liquid density. Information on liquid density can be inputmanually into the control system. Alternatively, the control softwarecan calculate the density based on temperature using establishedmathematical relationships.

The system works most effectively under isothermal conditions. It canhowever be used for reactions where the process temperature changes. Inthis case it is necessary to measure the heat capacity of the system asfollows:ΣM.Cp(M _(p) .Cp _(p))+(M _(c) .Cp _(c))where ΣM.Cp=heat capacity of the system (kJ/° C.)

-   -   M_(p).=mass of process fluid (kg)    -   Cp_(p)=specific heat of process fluid (kJ.kg⁻¹K⁻¹)    -   M_(c).=mass of equipment in contact with process fluid (kg)    -   Cp_(c)=specific heat of equipment in contact with process fluid        (kJ.kg⁻¹K⁻¹)

Conventional reactors have fixed area heat transfer surfaces (oroccasionally several elements such as separate sections on the bottomdish and walls). They perform most effectively with a high and constantflow rate of heat transfer fluid to the jacket (or coils). Processtemperature is controlled by varying the heat transfer fluidtemperature. In the preferred system, the area of the heat transfersurface may be varied according to the needs of the reaction (althoughsome variation in heat transfer fluid temperature can also be used) andthe area is varied by operation of the valve of the present invention.

The heat transfer fluid is applied to the control equipment at constantpressure and temperature. In some cases temperature can also be variedwhere it is necessary to increase the operating range.

A key requirement of reactors of this type is reliability. This isparticularly important in pharmaceutical applications where current goodmanufacturing practice (cGMP) dictates that the equipment operateswithin stated design parameters.

To provide a means of calibration and as a performance check, thereactor may be fitted with an electrical heater (or some other type ofreference heater). By supplying a measured current to the heater,reliable reference loads are provided for calibrating the system andchecking performance. In pharmaceutical applications, control and dataacquisition systems together with software should be validated to complywith cGMP standards.

In systems using a valve of the present invention where high precisionis required, the equipment incorporates both conventionalinstrumentation and process specific instrumentation to obtain theinformation for operation of the valve. These process specificinstruments operate at a higher than normal accuracy when compared toconventional instrumentation. FIG. 8 is a schematic illustration oftypical process instrumentation which consists of:

-   -   A process temperature RTD instrument (51)    -   A process temperature thermocouple instrument (52)    -   heat transfer fluid differential temperature instruments (48),        (49) and (50)    -   heat transfer fluid flow meter instruments (44) and (45)

For the process temperature RTD instrument (51) and the heat transferfluid differential temperature instruments (48), (49) and (50), matchingthe RTD sensor to the temperature transmitter can result in significantimprovements in control of the valve. The specific characteristic of anRTD sensor is unique to each device. By storing this information in thetransmitter improvements in accuracy of operation of the valve areobtained. The constants used in this technique are known as theCallendar-Van Dusen (CVD) constants.

By ‘process specific calibration’, (e.g. the optimum reactiontemperature) we mean that the instrument is calibrated specifically atthe normal process set point of an instrument and that the measuringsystem error is adjusted, such that at this operating point bestaccuracy is achieved (for a normally calibrated instrument, bestaccuracy is usually given at the maximum calibrated range, or at a pointdictated by the characteristics of the sensor). For example if a processis to be controlled at 35° C., instrument (51) would be calibratedacross a small range, say 25 to 45° C. Furthermore, the instrumentswould be calibrated at 35° C. and adjusted so that at this specificpoint the error of the measuring system is the minimum achievable. Onceinstalled and connected to the control system, the calibration of theinstrument loop can be verified as a complete installation and anycontrol system errors compensated for. The control system hardware isdesigned to minimise errors (precision components must be used) and thusoptimise accuracy. Similarly the instrumentation installation must besuch as to minimise measuring error.

The use of these additional steps, will allow maximum possiblecalibration accuracy to be obtained.

The process temperature thermocouple (52) can be calibrated in a similarmanner, but as it is used to measure rate of change of temperature asopposed to temperature, its overall accuracy, although still important,is less significant.

The heat transfer fluid differential temperature measuring instruments(48), (49) and (50) will also employ this same technique to ensure bestcalibration accuracy is achieved.

For the heat transfer fluid flow instruments (44) and (45) the techniqueis again similar. Calibration in this instance is carried out over asmall operating range with the emphasis on achieving the best accuracyat the preferred flow. By using multiple instruments calibrated overrelatively small operating ranges, e.g. 0-1, 1-2, 2-3 etc., asignificant improvement in accuracy is achieved than by using a singleinstrument calibrated over the range 0-3. Best accuracy is achieved byusing a suitably sized instrument with a normal flow of 80 to 90% of theinstrument span. Again, once installed in the field and connected to thecontrol system, the calibration of the instrument loop should beverified as a complete installation and any control system errorscompensated for. The control system hardware is again designed tominimise errors and thus optimise accuracy.

FIG. 9 shows a valve of the present invention in which (53) is the inletport for heat transfer fluid, (54 to 59) are the outlet ports, (60) isthe plunger. The Figure shows the plunger position with outlet port (54)open, outlet port (55) partially open and outlet ports (56 to 59)closed. (61) is the seal between the heat transfer fluid and hydraulicfluid employed in the actuator shaft (62) and (63) is the actuatorpiston whose position is determined by a bi-direction variable speedhydraulic pump (64) which drives the shaft up and down the valve body toopen and close the outlet ports. The arrows in FIG. 9 shows the flow ofthe heat transfer fluid.

FIG. 10 shows various options for the valve orifices (66 to 69) of thevalves (54 to 59) of FIG. 9. (66 to 69 A) is the plan view of theorifices and (66 to 69 B) shows the same orifices in section view.

Routine calibration of the heat measuring equipment may be carried outin several steps as follows:

The first step is zero calibration. For accurate operation, zerocalibration should be carried out for each type of process used. Thispermits the control system to compensate for any ‘non-process’ energychanges (e.g. heat gains and losses to the environment, energy gain fromthe agitator etc). The vessel is filled with liquid and the agitatorswitched on. It is then heated to the reaction temperature. When thetemperature is stable at the operating temperature, the heating/coolingsystem will function at a very low level to compensate for non-processenergy changes. The control system is zeroed under these conditions.

The second stage is to range and span the system. This is carried out byheating or cooling with a reference heater cooler. This may be in theform of an electrical heater or an independent heating/cooling coil.Heating. (or cooling) is carried out at several different energy inputlevels to range and span the system.

Alternatively the instruments may be tested individually in which casethe second step of the above process may not be necessary.

We have found that the reactor systems using the control valves of thepresent invention are extremely useful as batch chemical synthesisreactors. We have also found that the same size of machine may beemployed for development, pilot plant and full manufacturing purposes.

The preferred variable area heat transfer reactor is ideal for fastexothermic reactions, where it can operate as a small continuous flowreactor on processes hitherto conducted as batch reactions. Unlike largeconventional batch reactors, it is possible to operate in this mode asthe reaction is continuously monitored. Any fall off in conversionefficiency is detected immediately and forward flow is stopped. Thebenefits of operating in this mode are various. The capital cost of areactor for this type of application is substantially lower than aconventional reactor. In addition higher throughputs can be achieved.This type of equipment is also ideal for dangerous reactions as theinventory of reactants can be much smaller than that needed forconventional reactors. The equipment can also be programmed to stopreagent addition if unconsumed reactant starts to accumulate.

The reactors can also be used in slow exothermic reactions even wherelarge liquid volumes are held. In these reactors the data is obtained,analysed and used in a manner similar to the continuous reactordescribed above. The benefits of using this equipment for slow reactionsis that the addition rate of the components can be regulated to preventaccumulation of unreacted chemicals. It is also possible to identify theend point of the reaction which offers substantial savings in plantutilisation as the product can be transferred forward with theconfidence that it satisfies a key quality control objective. In somecases, accurate identification of end point also enhance product qualityand yield.

The rate at which heat can be transferred between the process fluid andthe heat transfer fluid is dictated (in part) by the overall heattransfer coefficient (U). The larger the value of U, the smaller theheat transfer area required. The U value may be calculated from threecomponents.

-   -   The heat transfer resistance through the process fluid boundary        layer    -   The heat transfer resistance through the coil wall    -   The heat transfer resistance through the heat transfer fluid        boundary layer

The boundary layers are the stagnant layers of liquid either side of thecoil wall. The faster the agitation (or liquid flow), the thinner theboundary layer. Thus high flow rates give better heat transfer. Alsoliquids with good thermal conductivity give better heat transfer throughthe boundary layers.

Heat transfer mechanism across the coil wall is similar, except (unlikethe boundary layers) the distance through which the heat has to conductis fixed. Higher heat transfer rates are achieved where the coilmaterial has high thermal conductivity. Higher heat transfer rates arealso achieved where the coil material is thin.

Thus a high U value requires both a thin coil material (with highthermal conductivity) and turbulent conditions in both liquids (the moreturbulent, the better). The higher the U value, the smaller the arearequired for heat transfer. This means a shorter heat transfer coil.

It is therefore preferred to use the thinnest walled coils possiblewithout compromising mechanical strength and corrosion tolerance. Atypical wall thickness would be ½ to 4 mm.

The material from which the coil is fabricated is not critical butshould be inert to the process fluid. Preferred materials include,stainless steel for non-corrosive organic fluids, Hastelloy C (22 or276) or similar alloys for most reactions using chlorinated solvents orother corrosive compounds. Tantalum and titanium would be used wherespecial corrosive conditions existed. In some applications othermaterials such as plastic, glass, glass lined steel or ceramics could beused.

The invention can be used in reactor systems which improve the operationof commercial chemical and physical reaction systems. It can howeveralso be used in the provision of considerably smaller reaction systemswith comparable commercial throughput. For example it may be used insystems which enable reduction of reactor size by a factor of 10 and, insome instances, a factor of 100 or greater. In particular it can beapplied to current commercial

-   -   batch organic synthesis reactions currently carried out in        reactors of 10 to 20,000 litres.    -   bulk pharmaceutical synthesis reactions currently carried out in        reactions of 10 to 20,000 litres.    -   batch polymerisation reactions currently carried out in reactors        of 10 to 20,000 litres.    -   batch synthesis reactions of 10 to 20,000 litres currently used        for unstable materials (compounds susceptible to        self-accelerating runaways)    -   batch inorganic synthesis reactions currently carried out in        reactions of 10 to 20,000 litres.

The techniques may also be useful in larger scale chemical andpetrochemical operations.

1. A valve for the control of the delivery of fluids to two or moreconduits in a cascade fashion wherein the valve has multiple outletports operating in a cascade wherein the outlet ports are opened and/orclosed according to a signal expressing the requirement for fluid in theconduits.
 2. A valve according to claim 1, in which activation isachieved by a single control system.
 3. A method for controlling theflow of heat transfer fluid to heat transfer coils comprising: operatinga valve which controls the delivery of fluids to two or more conduits ina cascade fashion wherein the valve has multiple outlet ports operatingin a cascade wherein the outlet ports are opened and/or closed accordingto a signal expressing the requirement for fluid in the conduits,wherein said valve is operated to provide fluid to selected coils orshut off fluid from selected coils according to the measurement of theheat released or absorbed by the reaction.
 4. The method according toclaim 3, in which the heating or cooling coils are part of a heatexchanger.
 5. The method according claim 3, in which the heat exchangeris part of a vessel for undergoing physical or chemical changes.
 6. Themethod according to claim 34, wherein the heat generated or released inthe reaction is measured by the heat absorbed by or released by thefluid as it passes through the reaction medium.